Roses use water to absorb nutrients from the soil. The amount of water required varies. Too much water will kill the plant.
[From The Complete Book of Roses, edited by John Mattock, p. 42:] There are very good reasons in a dry spring to water newly planed rose stocks... it is vital to obtain a good-sized plant as quickly as possible. The frequent use of water in an established rose bed is quite a different matter and is to be avoided. Established plants, if heavily watered for a lengthy period during the summer months, will put on gross soft growth which will not harden up enough to face the rigours of a severe winter.